A typical vehicle brake system includes an emergency/park brake apparatus that is used to hold the vehicle in position while it is parked, or to stop the vehicle in the event the primary braking system fails. In some modern vehicles, the emergency/park brake apparatus is electrically actuated. In such an electrically actuated brake apparatus, an electrical drive motor is used to drive a ball screw, or other drive device, to engage the brake. When electrical power is removed from the motor, however, spring forces inherent in the brake apparatus can cause back-driving of the drive device and drive motor, thereby releasing the brake. Vibration increases this inherent tendency.
What is needed, therefore, is an improved electrically actuated brake apparatus that can be locked against release when power is removed. It is also desirable that the brake assembly have provisions for unlocking and releasing the brake apparatus, should the drive motor or the power source connected to the drive motor malfunction.